Field of the Invention
This invention relates to a turbocharger for an internal combustion engine. More particularly, this invention relates to an oil drain in a turbocharger bearing housing in which the oil flows out along the outer edge of an oil drain leaving the center of the drain open. Air can flow between the bearing housing and the oil sump allowing for an equalization of air pressure. As a result of equalization of air pressure, oil drainage from the bearing housing is enhanced.
Description of Related Art
A turbocharger is a type of forced induction system used with internal combustion engines. Turbochargers deliver compressed air to an engine intake, allowing more fuel to be combusted, thus boosting an engine's horsepower without significantly increasing engine weight. Thus, turbochargers permit the use of smaller engines that develop the same amount of horsepower as larger, normally aspirated engines. Using a smaller engine in a vehicle has the desired effect of decreasing the mass of the vehicle, increasing performance, and enhancing fuel economy. Moreover, the use of turbochargers permits more complete combustion of the fuel delivered to the engine, which contributes to the highly desirable goal of a cleaner environment.
Turbochargers typically include a turbine housing connected to the engine's exhaust manifold, a compressor housing connected to the engine's intake manifold, and a center bearing housing coupling the turbine and compressor housings together. A turbine wheel in the turbine housing is rotatably driven by an inflow of exhaust gas supplied from the exhaust manifold. A shaft rotatably supported in the center bearing housing connects the turbine wheel to a compressor impeller in the compressor housing so that rotation of the turbine wheel causes rotation of the compressor impeller. The shaft connecting the turbine wheel and the compressor impeller defines an axis of rotation. As the compressor impeller rotates, it increases the air mass flow rate, airflow density and air pressure delivered to the engine's cylinders via the engine's intake manifold.
The turbine wheel and the shaft of a turbocharger rotate very fast. The rotation speed of a turbocharger shaft depends upon the size of the turbine wheel and smaller turbine wheels can rotate faster than larger wheels. A turbocharger turbine wheel and shaft used in conjunction with an internal combustion engine may reach circumferential tip speeds of 530 meters per second. The turbine wheel operates in a high temperature environment and may reach temperatures as high as 1922° F. (1050° C.). This heat is conducted by the turbine shaft to the bearing housing. The rapid rotation of the turbine shaft creates frictional forces which further heat the bearing area. Thus, there is a need for lubrication and cooling of the turbocharger shaft and bearing housing. In an oil lubricated turbocharger, oil is pumped to the shaft to provide the necessary lubrication and cooling. In an automotive turbocharger the flow rate of the oil to the bearing can be as a high as 1 gallon per minute. Oil must also be removed from the bearing housing because if it builds up in the housing it could leak through the seals into the compressor housing or the turbine housing. In addition, if the oil remained in the turbocharger bearing housing, it could degrade due to overheating and could even form coke. Generally, oil is not pumped out of the turbocharger housing bearing housing but flows out of the bearing housing by gravity. The oil flows to the engine oil sump where it is cooled and then pumped to lubricate the engine and the turbocharger.
U.S. Pat. No. 7,811,001 and U.S. Pat. No. 7,387,445 relate to a bearing housing. The bearing housing includes a chamber with out-take for oil scavenging. The out-take extends across a chordal arc of the chamber. A portion of an outer wall adjacent to the out-take has a spiral divergence.
U.S. Pat. No. 7,476,090 relates to a turbocharger for an internal combustion engine which includes a center housing connected to a turbine housing and a compressor housing. A shaft is in a bore of the center housing. An oil supply passage is in fluid communication with the bore. An oil drain passage is in fluid communication with an oil cavity and the bore. A vent passage is in fluid communication with the oil cavity and an internal volume of the internal combustion engine. Oil flow passes through the first passage and the drain passage during operation of the internal combustion engine. A first pressure of air in the oil cavity is about equal to a second pressure of air in the internal volume of the internal combustion engine. To avoid an increase of the pressure inside the center housing above the low pressure in the internal volume, a pressure vent tube fluidly connects the center housing with the internal volume. The pressure vent tube ensures that the pressure inside the center housing will be equal to the pressure in the internal volume. By equating the pressures, smooth flow of oil is ensured in the center housing.